netdev - Re: [PATCH net v3] net/sched: cls_api: Fix nooffloaddevcnt counter when indr block call success

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Message-ID: <CAJ3xEMgWr9u2W4pjLj5-bkcJ9-wCySyjtzFLSwQGGmPsigEUkg@mail.gmail.com>
Date:   Tue, 24 Sep 2019 13:33:37 +0300
From:   Or Gerlitz <gerlitz.or@...il.com>
To:     wenxu <wenxu@...oud.cn>
Cc:     John Hurley <john.hurley@...ronome.com>,
        Pieter Jansen van Vuuren 
        <pieter.jansenvanvuuren@...ronome.com>,
        Oz Shlomo <ozsh@...lanox.com>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        David Miller <davem@...emloft.net>,
        Linux Netdev List <netdev@...r.kernel.org>,
        Roi Dayan <roid@...lanox.com>,
        Paul Blakey <paulb@...lanox.com>,
        Jiri Pirko <jiri@...lanox.com>
Subject: Re: [PATCH net v3] net/sched: cls_api: Fix nooffloaddevcnt counter
 when indr block call success

On Mon, Sep 23, 2019 at 5:21 PM wenxu <wenxu@...oud.cn> wrote:
> 在 2019/9/23 17:42, John Hurley 写道:
> > On Mon, Sep 23, 2019 at 5:20 AM wenxu <wenxu@...oud.cn> wrote:
> >> Hi John & Jakub
> >>
> >> There are some limitations for indirect tc callback work with  skip_sw ?
> >>
> > Hi Wenxu,
> > This is not really a limitation.
> > As Or points out, indirect block offload is not supposed to work with skip_sw.
> > Indirect offload allows us to hook onto existing kernel devices (for
> > TC events we may which to offload) that are out of the control of the
> > offload driver and, therefore, should always accept software path
> > rules.
> > For example, the vxlan driver does not implement a setup_tc ndo so it
> > does not expect to run rules in hw - it should always handle
> > associated rules in the software datapath as a minimum.
> > I think accepting skip_sw rules for devices with no in-built concept
> > of hardware offload would be wrong.
> > Do you have a use case that requires skip_sw rules for such devices?

> When we use ovs to control the tc offload. The ovs kernel already provide the software
> path rules so maybe user don't want other soft path.

this (programming the rule to both tc and ovs kernel DPs) is a choice made by
the ovs user-space code and could change later. Actually, for complex use
case such as connection tracking, there might be cases when multiple tables
are used, when the 1st packet/s would jump before hw to sw TC tables, so
using skip_sw will likely not to work and we'll get bug reports. The production
TC configuration we use/recommend with for overlay networks e-switching
is "both" (== "none", i.e none of skip_sw or skip_hw).

> And with skip_sw it can be easily distinguish offloaded and non-offloaded rules.

per tc rule, the kernel reports on offloaded vs not offloaded
packet/bytes, so the
info is there. In the system level, I don't think it's good that on
point A in time
we blocked skip_sw rules for tunnel devices and at point B we enabled it for no
real/good reason, I vote for blocking it again, since as Pieter
explained disallowing
this is not consistent with the kernel SW model on the receiving side.